Many marine propulsion systems, such as marine outboard engines, have a gear cases assembly. One of the functions of the gear case assembly is to transmit torque from the engine to the propeller or impeller of the propulsion system. The gear case assembly includes a gear case that houses various shafts and gears used to achieve this torque transmission.
The components housed in the gear case used for the torque transmission are typically bathed in lubricant. During operation of the propulsion system, a pump circulates the lubricant through various chambers and passages formed by the gear case and housing the various components.
In order to initially fill these chambers and passages and later replace the lubricant in these chambers and passages, some gear case assemblies are provided with one upper and one lower lubricant filling port. Each port fluidly communicates a corresponding one of the chambers or passages with the exterior of the gear case and is closed by a plug. To fill the chambers and passages with lubricant, the plugs are removed from the filling ports and lubricant is pumped through the lower lubricant filling port. When lubricant begins to come out of the upper lubricant filling port, the chambers are considered to be filled with lubricant and the plugs are placed in the lubricant filling ports. However, as will be explained below, the chambers are not actually full of lubricant. To remove the lubricant from the chambers and passages, the both plugs are removed and lubricant is drained out.
When filling the chambers and passages with lubricant, the flow of lubricant in one or more of the chambers can be obstructed by various constraints. This is the case for example for the driveshaft passage that houses a portion of the driveshaft. Flow of lubricant through the driveshaft passage may be partially obstructed by the various bearings positioned between the driveshaft and the wall of the driveshaft passage. When filling the chambers and passages with lubricant as described above, the lubricant flows more quickly up unobstructed or less obstructed chambers and passages than passages that have obstructions such as the driveshaft passage. As a result, the pumped lubricant may reach the upper lubricant filling port even though the driveshaft passage is only partially filled with lubricant. This means that when the plugs are replaced in the lubricant filling ports, a volume of air is still present in the driveshaft passage.
Over time, the lubricant levels off in the gear case and some air remains present above the lubricant. The final level of lubricant depends on the overall volume of the chambers and passages. In gear case assemblies where this volume is relatively large, the final level of lubricant is typically high enough to bathe in lubricant all of the components that need to be lubricated. However, in gear case assemblies where the overall volume of the chambers and passages is relatively small, the final level of lubricant can be too low to bathe all of these components in lubricant. One example of a gear case assembly where the overall volume of the chambers and passages is relatively small is a gear case assembly in which the transmission actuator includes an electric motor disposed in the gear case. The electric motor has to be isolated from the chambers and passages in which lubricant is present, thus reducing the volume that could otherwise be available for lubricant.
One solution consists in filling the chambers and passages in multiple steps. In this solution, the chambers and passages are filled as described above, except that the plugs are not placed in the oil filling ports right away, and some time is then allowed to lapse to give time to the lubricant to level off. More lubricant is then pumped in the chambers and passages until it starts coming out of the upper lubricant filling port again, and more time is then allowed to lapse to give time to the lubricant to level off. This step is repeated until it is determined that all of the chambers and passages are actually full of lubricant at which point the plugs placed in the oil filling ports. As would be appreciated, this method is very time consuming.
There is therefore a need for a gear case assembly that permits the filling of the lubricant chambers and passages in the gear case while limiting the amount of air remaining in the lubricant chambers and passages at the end of the filling operation.